IGNITION GAP ARRANGEMENT

Abstract: The invention relates to an arrangement in such ignition gaps or channels as are used in combustion devices, for example internal-combustion engines, to impart to an injected finely-divided particulate fuel a temperature sufficient for ignition, heat being transferred from the heated walls for the ignition gaps or channels. The novelty of the invention resides in that the ignition gap or gaps (2) are zigzag-shaped or otherwise formed of two or more substantially straight sections connected at an angle to each other.

Description: IGNITION GAP ARRANGEMENT Technical Field This invention relates to ignition gaps of the type used in e.g. internal-combustion engines to impart to an injected fuel, preferably in the form of a powder, a tem¬ perature enabling the required combustion. Prior Art Swedish Patent Specification 8202835-8 describes an ignition gap device for diesel engines, where wood powder is supplied into the ignition gaps and caused to impinge on the heated gap walls and be progressively ignited. Background of the Invention The major problem in the operation of internal-com- bustion engines employing solid fuels in powder form is the ignition delay. In diesel engines, the ignition delay is defined as the time elapsing from the moment the fuel is injected into the combustion chamber until it is ignited. Summary of the Invention The invention, which has been conceived to enable controlled reduction of the ignition delay and to make more efficient the ignition of the powder, is character¬ ised in that the ignition gaps are arranged in a zigzag configuration, and that the ignition gaps are provided in optional lengths by using a modular technique that can be adapted to prevailing requirements. Description of Embodiments Preferred embodiments of the arrangement according to the invention will be described in more detail hereinbelow with reference to the accompanying drawings, in which Fig. 1 is a schematic partial cross-section showing the possible design of an ignition gap section, Fig. 2 is a schematic cross-section showing the design of a slightly modified ignition gap device, Fig. 3 is a general view, partly in section, showing how the ignition gap device is integrated in an injec¬ tion mechanism, Fig. 4 is a cross-section showing how three ignition gap plates of different hole configuration are joined together to form ignition gaps extending in zig¬ zag, Fig. 5 is an end view of the upper plate in Fig. 4, Fig. 6 is an end view of another plate embodiment, Figs 7, 8 and 9 are cross-sections of the plate in Fig. 6, taken along the lines A-A, B-B and C-C, respectively, and Fig. 10 is an extended view taken along the radius r in Fig. 9 through three plates arranged as in Fig. 4. Description of Embodiments Fig. 1 schematically illustrates the general idea behind the invention, which resides in that the fuel, i.e. usually the powder, is caused during its way up to the injection nozzle in the combustion chamber, to follow a zigzag-shaped path created by ignition gaps or channels 2 formed of several plates or modules 1, each of which com¬ prises one or more channel or gap sections which, when the plates or modules have been placed adjacent each other, form one or more zigzag-shaped gaps or channels, in that the channel or gap sections in the respective plate or module have different directions, but with the inlets and outlets located in the same positions as the inlets and the outlets of adjacent plates or modules. In the embo¬ diment of Fig. 1, the mutual directional deviation of the sections 2 in the three plates 1 is about 140°. The plates or modules 1 which, as will appear below, will be subjected to high temperatures, are consequently made of ceramics, whose end surfaces 3 are accurately ground and lapped such that they will seal against each other without the need of additional sealing devices and together define the channels or gaps in a substantially leakproof manner. Fig. 2 shows how a number of plates 1 have been arranged adjacent an injection nozzle 4 opening over a piston 5 in the combustion chamber 6 of a diesel engine. In this case, the end plates la and lb have spherically- domed surfaces 7 accurately mating with surfaces 8 of complementary dome shape on a part 9 and 10, fixed to the engine and arranged at the injection mechanism, respec- tively. The part 10 is provided with a movable gland seal 11 taking up the temperature movements in the plates. The spherical end plates facilitate mounting. This Figure also shows a heating coil or winding 12 serving to heat the plates 1 during the starting phase. For clarifying purposes, a description of the prefer¬ red fuel, being in powder form, will now be given. In the manufacture of fuel powder for internal com¬ bustion engines, the fuel is ground and sifted. In this case, use may be made of beater mills, ball mills, cylpebs mills and pinned disc mills, as well as vacuum mills. Sifting takes place in wind sifters, basically designed as a centrifugal fan where a gas laden with powder is caused to flow through the fan from the peri¬ phery towards the centre. This means that only very small particles can pass the wind sifter. By varying the flow through the fan and its speed of rotation, it is possible to obtain a very fine powder. Fig. 3 is a general view partly in section showing how the arrangement according to the invention is inte- grated in an injection mechanism. The plates fitted to each other are designated 1, and those having spherical end surfaces 7 are designated la and lb, respectively. The injection nozzle is designat¬ ed 4, and the injection mechanism feeding and portioning the fuel is generally designated 13. The heating coil is designated 12. Other components in this Figure are illu¬ strated for clarifying purposes only. As will have been appreciated, it is vital that the plates 1 be joined together in a most accurate manner. In order that the ignition gaps should function pro¬ perly, the temperature must be at least 900°C. The engine runs with a minimum emission of smoke when the temperature is 1100°C. Since metallic materials do not withstand such high temperatures, ceramics must be used. For working ceramics, diamond tools, such as silicon nitride and aluminium oxide, are required. The cheapest way of producing ceramics is to compres¬ sion-mould powder which is then sintered at a high tempe¬ rature. One possibility is to presinter the compression- moulded powder and perform turning and drilling before the final sintering takes place. In the diesel engine describ- ed above, the zigzag-shaped ignition gap is formed of ten parts having straight channels with 140"-bends and an ignition gap diameter of 6 mm. The zigzag-shaped ignition gap is obtained from a number of round plates having angled holes. As mentioned above, the plates have been ground and lapped such that, when pressed against each other, there is but negligible leakage between them, see Fig. 1. Figs 4 and 5 show a modified design of plates 1, the shape of the channel or gap sections varying in the dif- ferent plates. This embodiment, like the others, can be compressed to final shape before sintering, the only remaining operation being grinding and lapping. Figs 6, 7, 8 and 9 show yet another plate design which can also be compressed to final shape before sinter- ing and subsequent grinding and lapping. In this embodi¬ ment too, a different channel or gap shape is obtainable. Fig. 10 is an extended schematic view showing how the transport paths for the fuel are formed and how they are given a pronounced zigzag configuration, entailing that the fuel particles are forced to repeatedly impinge on the gap or channel walls, which are strongly heated, which results in the ignition of the fuel when injected into the combustion chamber. Zigzag-shaped ignition gaps according to the inven- tion can be used for igniting all pulverulent fuels made from wood, straw, grass, bagasse, peat, coal and brown coal for firing furnaces, internal-combustion engines, both Otto and diesel engines, as well as gas turbines. The fuel which is undoubtedly the best is Eucalyptus Teriti- cornis because of its extremely low ash content. Depending on its habitat, this tree species has less than 0.03% ash based on the dry weight of the wood. Practical tests have shown that if the fuel particles are smaller than 16 μm with a normal distribution around 8 μm and the solid fuel consists of wood powder that has been hydrolysed (with the aid of superheated formic acid steam at 200°C for 2 h at atmospheric pressure), the ignition delay becomes only 15° at a speed of 3600 rpm if zigzag-shaped gaps or channels having a length of about 200 mm and a diameter of 6 mm are used. The reason why a zigzag-shaped channel or gap is more efficient than a conical one is that the larger particles will impinge on the hot walls a considerable number of times when passing through the ignition gap compared with an expanding gap as described in Patent 8202835-8.

Claims: CLAIMS 1. An arrangement in such ignition gaps or channels as are used in combustion devices, for example internal- combustion engines, to impart to an injected finely-divid¬ ed particulate fuel a temperature sufficient for ignition, heat being transferred from the heated walls of the igni¬ tion gaps or channels, c h a r a c t e r i s e d in that the ignition gap or gaps (2) are zigzag-shaped or other¬ wise formed of two or more substantially straight sections connected at an angle to each other. 2. An arrangement as claimed in claim 1, c h a r ¬ a c t e r i s e d in that one or more ignition gaps are formed of a number of plates (1) having substantially inclined through openings (2) and arranged one adjacent the other with the ends of the openings corresponding with each other, the openings (2) of adjacent plates having deviating directions. 3. An arrangement as claimed in claim 2, c h a r ¬ a c t e r i s e d in that in the case of a number of plates (1), each having at least one through opening (2), the inclination of the through opening deviates from the normal to the plane of the respective plate by an angular value of the order of 20°. 4. An arrangement as claimed in claim 3, c h a r ¬ a c t e r i s e d in that the plates (1) have a thickness of the order of 20 mm. 5. An arrangement as claimed in claim 1, 2 or 3, c h a r a c t e r i s e d in that the abutting surfaces (3) of the plates (1) are ground and lapped or otherwise given such a smoothness as to achieve the required tight¬ ness. 6. An arrangement as claimed in claim 5, c h a r - a c t e r i s e d in that the plates consist of a cera¬ mic material, that the plates are given the desired shape prior to sintering, and that only the end surfaces (3) are ground and lapped after sintering. 7. An arrangement as claimed in claim 1 or the fol¬ lowing claims, c h a r a c t e r i s e d in that at least the two outermost plates (la, lb) in a stack of plates exhibit spherically-domed smoothed end surfaces adapted to engage surfaces of complementary shape in support and compression means. 8. An arrangement as claimed in claim 7, c h a r - a c t e r i s e d in that the compression means comprises a gland sealing device, against which the stack of plates (1) is applied, and that the compression means suitably is provided with means for cooling it. 9. An arrangement as claimed in claim 8, c h a r - a c t e r i s e d in that at least one flange device acting on one end of the stack of plates (1) is operable by an external pressure striving to hold the plates (1) compressed. 10. An arrangement as claimed in any one of the pre- ceding claims, c h a r a c t e r i s e d in that the material of the plates (1) is adapted to withstand a tem¬ perature of the order of 1250°C and an internal pulsating pressure of the order of 1-200 bar.

Inventors: ABOM JAN, AABOM, JAN
Applicants: AABOM JAN, TOERNQVIST BENGT GUNNAR, AABOM, JAN, TOERNQVIST, BENGT, G.
Application year: 1994
Main classification: F02B9
IPC codes: F02B9, F02B19, F02B45, F02M21